B&W Reversal Processing - WOW

Does anyone know the formula for bleach with Pottasium Dichromate?

htmlguru4242 said:

The bleach is Sodium Dichromate and an acid (sulfuric, I believe). Potassium dicromate can be used as well if you're mixing it for yourself.

Click to expand...

htmlguru4242 said:

And to Matt, I have heard of processing reversal emulsions as negs. as well, though I've heard that the results are increased grain and speed loss. I've never tried this though, actually.

And when you say "standard 8mm", are you talking about the 16mm double 8mm that's flipped halfway through & slit in processing, or the actual 8mm wide on a daylight spool stuff?? What film was it, by the way?

From what I've head about home processing 8mm or 16mm is to do it in either a bucket or using a rewind tank, though the reel apparently gives great results.

Click to expand...

I was using Kodak PlusX 100ASA. It is a new emulsion which replaces their old PlusX which was rated at 80ASA (I think). This little Bell & Howell fits into the palm of your hand and had a three lens turret with wide angle, normal and telephoto primes all made by Taylor, Taylor and Hobson. The wide angle is a really superb lens and is excellent for ski and snowboard shots where you can hand hold without the need to look through the viewfinder whilst "on the move".

And if you wipe out and get snow all over it? you just wipe it off and carry on - this camera is like a brick and virtually indestructable! All metal construction yet quite light to hold.

Matt.

Bleach formulas vary, though they are approximately:

15g potassium dichromate
12ml Sulfuric Acid (battery acid is reported to work OK)
1L water

This hsould work, adjust it as you need to.

Potassium permanganate may be used, but I've never actually used it. I've heard that dichromate is better, though the safety issue is a problem. Permanganate is much less dangerous. Potassium ferricyanide, or even copper sulfate may be used as well, though I'm not sure of the amounts. All of these chemicals are available through Photographer's Formulary, B&H (which orders through Photo. Formul.) and chem. supply houses here in the US. I'm not sure about anywhere else, though.

htmlguru4242 said:

Farmer's Reducer will not work for hte bleach; it contains thiosulfate (fixer) which will remove the halides from the film. Ths, regardless of what you do afterwards, will leave you with blank film.

As to developer choices, anything'll work, though some work significantly better than others. I've seen reccomentations to use 1:1 diluted Dektol for 6 minutes for first. dev.

The bleach is Sodium Dichromate and an acid (sulfuric, I believe). Potassium dicromate can be used as well if you're mixing it for yourself.

Click to expand...

Thanks for the clarification. I just remembered that Farmer's reducer is a bleach and had no idea what it might do. Lesson learned.

So, if any developer will work, by how much are you supposed to over develop the film the first run, and do you develop for the normal time the second time? It just seems that from what people have been saying, you need to build up sufficient density the first development, so that you get a decent positive. Any suggestions?

Drew

I just popped over to Ilford and looked at their guidlines for reversal developing. They use their paper developer for about 3X the normal development you would give the film if you used the paper developer. Does this 3X "rule" work for any developer? Or is it just another arbitrary rule?

They also give recipes for the bleach solution and the clearing solution. Just to let people know. Your thoughts are appreciated.

Drew

The Ilford PDF method works well, but you may need to do some fine-tuning. The 3X factor is just a coincidence in this case. The actual first dev time will depend on the EI, dilution, and the amount of sodium thiosulfate in the first developer (remember that Ilford's first developer is not just straight paper developer).

The bleach and clearing solution Ilford gives do work though the emulsion will tend to become damaged if you are not careful to keep ALL of the processing solutions at the same temperature.

Jordan said:

I've been thinking about easy ways to get at reversal bleaches for a while now, and I think that the tray cleaner idea is a good one.

Click to expand...

Jordan,

Tray Cleaner is to remove the silver deposits that gets on a tray? That would be Potassium Dichromate or Potassium Permanganate with sulfuric acid right? Wouldn't it just be easier to buy a bag of permaganate from an acquarium supply store?

regards,
Jay Cordaro

jason314159 said:

Tray Cleaner is to remove the silver deposits that gets on a tray? That would be Potassium Dichromate or Potassium Permanganate with sulfuric acid right? Wouldn't it just be easier to buy a bag of permaganate from an acquarium supply store?

Click to expand...

It all depends on how easy it is to find these chemicals where you live. The tray cleaner (acidified potassium dichromate, from what I've read) is basically bleach "ready-to-use" -- it does clean off silver deposits, as you mention. Potassium permanganate is also an effective bleach, but I've found that it softens the emulsion to the point of damage unless you are very careful. (Alessandro Serrao has more data on this.)

I've never checked local aquarium suppliers for KMnO4, and I'm pretty sure that my local darkroom suppliers don't carry tray cleaner, so I buy these materials from JD Photochem anyway.

One disadvantage to permanganate bleaches is that they are not stable. You need to mix the permanganate solution up with acid immediately before use. When I used permanganate bleach I accomplished this by keeping two stock solutions (one KMnO4, one NaHSO4) on-hand. Dichromate bleaches are stable in their acidified form, so you have to "handle less acid" as it were.

Both bleaches are extremely corrosive and you need to avoid skin contact at all costs. Permanganate is much less toxic by ingestion and is easier on the environment than dichromate, but you have to dump the permanganate after each use (the acidified bleach is not stable) whereas dichromate can be re-used until it's exhausted.

Jordan said:

It all depends on how easy it is to find these chemicals where you live. The tray cleaner (acidified potassium dichromate, from what I've read) is basically bleach "ready-to-use"

Click to expand...

OK, I understand now, sounds convenient. Potassium permanganate is used to kill algae growth and parasites in large fish tanks and fish ponds. Needless to say this stuff is probably not USP. I am not a chemist although I took organic chemistry and lab in engineering school...working with and disposing of a chromium compound makes me nervous...

Thanks for the tips on using permanganate, I will be careful with the emulsion. I have heard it can stain the film as well. I have a fume hood I can use at work (we use HNO3 and H2SO4 to decapsulate semiconductors from their packages). I was planning of going in on a saturday mix the bleach in the morning and then do reversal developing all afternoon and disposing of the chemicals at the end...

-JLC

Matt5791 said:

Interesting how you have processed the "negative" emulsions as reversal though. I have heard of people processing the reversal emulsions as negative too!

Matt

Click to expand...

The films are the same in terms of chemical make up - tho I think the reversal films use a different grain structure so as to maximise the leftover grain density after the bleach and re-exposure -

I know that if you process reversal b&w as neg it comes out very grainy (done it with some Plus-X), the bleach usually removes these large grains.. perhaps the bleach works better on it or at least the large grains are exposed in-camera in the first instance leaving the smaller grains for the reversal ...


also, similar discussions here:

(there was a url link here which no longer exists)